Try this resource;http://www.nsvrc.org/contact/request-assistance
Statistics can show much information, but, let me ask, what would happen if you Did find support that suggested the perpetrator that hurt your husband could possibly hurt your niece and nephew. What would you do? How would you intervene? Could you disclose the abuse to the "other" brother, helping him to understand that his children are in danger? Would he believe you? Could you convince your husband now is the time to disclose to his family the abuse? Chances are they know something is already wrong, but they do not know what it is. Would they trust him?
Preparing to confront and disclose can be a rewarding experience, for the survivor, or it can crush the cathartic experience. There is a wonderful article that details the steps of this stage of recovery. http://www.malesurvivor.org/ArchivedPages/singer3.html
Finally, understand the burden that has been placed upon you, love. As the supporter, you may not have physical proof, and only one witness that can verify the account. This is a "he said, she said" accusation, and it can undermine your reliability if the survivor is not ready to disclose, or should the perp categorically deny it. Intervention is a difficult process, love, I am encouraged by your desire to protect potential targets of the perp, as well as supporting the survivor. Please plan out your steps, this kind of thing is best when the survivor is ready.
Be careful, plan you interventions and support carefully. You will be successful, but it is a process, as a marathon with checkpoints versus an all out sprint. Make sure your are clear about your actions so that you can continue to be a source of safety and encouragement.